Study On Diaphragm-Deformation-Based Extrinsic Fabry-Perot Interferometric Optical Fiber Low Pressure Sensor

Pressure sensors have many important applications in many areas,such as the liquid level pressure of petroleum-reservoir storage facilities,the osmotic pressure of reservoir-dam,the detection of acoustic signals in extraordinary environment and pressure monitoring in organisms.Monitoring high-sensitively and accurately of the pressure in these fields are of great importance to the safety production and enhancement of economic benefits.Optical fiber sensors have become the research focus of pressure monitoring in the above-mentioned fields because of the unique advantages of intrinsic safety,high sensitivity,immune to electromagnetic interference,small size,light weight,and so on.In this dissertation,structure design,fabrication technology and materials selection for DEFPI(Diaphragm-Deformation-Based Extrinsic Fabry-Perot Interferometric)optical fiber pressure sensors were studied.The main research works of this paper are as follows:We analyzed the basic principle,the deformation mechanism of diaphragm,and the pressure measuring principle of a DEFPI optical fiber sensor in detail.We also discussed the influence factors of the output signal quality of a DEFPI fiber-optic sensor and the interderence signal demodulation algorithm of F-P fiber-optic sensor.In addition,we analyzed the operation point stabilization when the dynamic pressure signals are detected by interference-intensity demodulation method.In order to improve the DEFPI optical fiber sensor performance,we studied the interaction between fused silica and laser,and proposed a kind of full-laser-welding DEFPI optical fiber sensor based on fused-silica.Combined with advanced MEMS control system,the laser welding optical systems were constructed,and the CO2 laser heat conduction welding and deep melting spot welding technique are studied for welding of fused-silica glass.The welding of ultra-thin fused-silica diaphragm with 30?m-thick is realized employing the laser heat conduction welding technique.And,the method of laser deep penetration spot welding was proposed for the first time,which is employed to fix the optical fiber on the inner wall of the fused-silica ferrule.At the same time,a vent hole for F-P cavity was reserved between the optical fiber and the fused-silica ferrule in the process of laser welding.The vent hole plays an important role in reducing the temperature-pressure cross-sensitivity.Comparison of laser circular welding for the sensor,laser deep penetration spot welding can effectively improve the performance of sensor,and reduce the preparation technique.And then,we researched the feasibility of DEFPI optical fiber low pressure sensor in the practical application.Firstly,the sensor applied to measure the water-level of 12 meters possesses 52.5nm/m of sensitivity,6.8Pa of resolution,0.06%F.S.of hysteresis error,and temperature sensitivity of 0.013nm/?.Aiming at the application in the environments with the large temperature change,we employed the multiplexing method of FBG(Fiber Bragg Grating)and F-P(Fabry-Perot)cavity to compensate the measurement error.After packaged in 316L stainless steel,the measurement error was effectively compensated within 100?.Secondly,aiming at the monitor of the dam osmotic pressure in the range from 0 to 1 MPa,we modified the parameters of fused silica structure sensor.The research results show that thesensor has a resolution of 2.3Pa,a hysteresis error of 0.021%F.S.,a fluctuation range oflong-term stability of 0.8kPa.Thirdly,to solve the problem of operation poin stabilization formeasuring dynamic pressure,the scheme based on ASE(Amplified Spontaneous Emission)source and tunable F-P filter is designed,and used to measure the ultrasonic wave signal with 40 kHz in transformer oil.The sound pressure sensitivity of a sensor is 6.59mV/kPa.To measure the pressure in organisms,we proposed the chitosan with biocompatibility to act as diaphragm of sensor,and the method of modifing chitosan by glutaraldehyde active group cross-linking.Also,we designed the preparation technique of cross-linking chitosan diaphragm and the robust bonding method with the fused silica ferrule end face.The chitosan pressure sensitivity diaphragm with good compactness,900MPa of Young's modulus,1.73 of refraction index,and good adhesion were prepared,buliding the chitosan-based DEFPI optical fiber low pressure sensor.For the monitoring of the environment of simulating intracranial pressure,in the range from 0 to 24.4kPa,the sensor possesses a high sensitivity of 25.79nm/kPa,a resolution of 1.2Pa,a hysteresis error of 0.16%F.S..Considering the change of density and the readability error of water level measurement,the measurement error is 0.04%F.S..The fluctuation range of long-term stability test of 15 days is 0.121kPa.